This invention relates to a plasmatron-catalyst system which can maximize hydrogen yield and decrease the amount of carbon monoxide.
The pending U.S. application mentioned above, of which this application is a continuation-in-part, discloses and claims the use of a rapid response plasmatron for converting hydrocarbon fuels into hydrogen-rich gases. This process may be carried on-board vehicles.
Converting hydrocarbon fuels into hydrogen-rich gas (reforming) can be achieved with a plasmatron reactor. There are many advantages of using a plasmatron in the reforming process. Advantages include fast response (less than one second), adequate conversion into hydrogen-rich fuel, compactness (high hydrogen productivity), robustness (stable process), and the ability of the plasmatron to use many fuels, including hard-to-reform gasoline, diesel and biofuels.
For internal combustion applications, the hydrogen purity is not of great importance. High conversion efficiency into hydrogen is not necessary, since the low weight hydrocarbons that accompany the hydrogen produced by the plasmatron are also good fuels for use in internal combustion engines. More important is to minimize the energy consumed in the plasmatron during the reforming process.
U.S. Pat. Nos. 5,425,332 and 5,437,250 disclose plasmatron-internal combustion engine systems and the teachings of these two patents are incorporated herein by reference. Plasmatrons of the type used in the present invention are described in detail in these two patents.
Partial oxidation is a preferred method of reforming. An advantage of partial oxidation is that it eliminates the need for storing additional liquids on-board vehicles. Also, a fraction of the fuel is reformed in order to allow the introduction into the cylinder of an engine hydrogen-rich gas to improve the combustion process. Since the intention of the prior art is not to reform all of the fuel, the issues of efficiency, although still relevant, have not heretofore driven the design of a plasmatron system.
The previous application discloses the use of plasma catalysis on-board vehicles. The process of converting the hydrocarbon into hydrogen rich gases by the use of plasma catalysis addresses mainly the energy requirement in the plasmatron in the reformation process. Plasma catalysis, as used for applications in internal combustion engines, can decrease the electrical energy requirement. The prior art does not suggest the use of catalysts to maximize hydrogen yield nor to decrease the amount of CO (carbon monoxide) that is produced in the partial oxidation process (The hydrogen yield is defined as the ratio of the hydrogen in the reformats to the amount of hydrogen content in the fuel).
The prior art does not extend plasma catalysis into the context of fuel cell vehicles and stationary fuel cells in which very high hydrogen yields and low energy consumption are required.
The requirements on a reformate for fuel cell applications are very different from those for use of hydrogen rich gas in internal combustion engines. As described above, for application to internal combustion engines, it is not necessary to have high yields, a very efficient process or very clean gas. As used herein, clean gas is defined to be gas with small concentrations of CO, since CO is a poison to some types of fuel cells that are presently being considered for both stationary and vehicular applications, of which the PEM fuel cell is the most advanced candidate. U.S. Pat. No. 5,409,784 discloses plasmatron/fuel cell combinations and the teachings of this patent are incorporated herein by reference.
The prior art also does not disclose the possible use of water/steam in the reforming process.
In one aspect, the plasmatron-catalyst system of the invention for generating hydrogen rich gas includes a plasmatron and at least one catalyst for receiving an output from the plasmatron to produce hydrogen rich gas. The catalyst is located at such a position downstream from the plasmatron as to be activated by the hydrogen and radicals produced by the plasmatron. In a preferred embodiment, the plasmatron receives as an input air, fuel and water/steam. The plasmatron may also receive exhaust gas from an engine or fuel cell. It is preferred that the at least one catalyst receive as an input air, fuel and water/steam. The catalyst may also receive exhaust gas from an engine or fuel cell.
In another embodiment, the at least one catalyst includes a heat exchanger in heat exchange relation with the catalyst to preheat the air, fuel and water/steam. One embodiment includes a plurality of catalyst sections wherein each catalyst section receives additional air, fuel or water/steam.
In another aspect, the plasmatron catalyst system further includes a fuel cell for receiving the hydrogen rich gas, the hydrogen rich gas having reduced CO content. The fuel cell may be in a vehicle or in a stationary setting.
In another embodiment, the plasmatron is followed by fuel injection system for a partial oxidation process, the fuel injection system followed by a catalyst for improved yields, the catalyst followed by water/steam injection and a water-shift reformer catalyst whereby hydrogen concentration is increased and CO concentration is decreased. In any of these embodiments, the catalyst may be a water-shifting catalyst. The catalyst may also be a partial oxidation catalyst or a steam reforming catalyst. In yet another embodiment, the catalysts are a combination of partial oxidation, steam reforming or water-shift catalyst with possible addition of water/steam in between adjacent catalytic regions.
In another embodiment, the steam reforming catalyst is followed by a water-shifting catalyst, with or without additional water/steam injection prior to the water-shifting catalyst.
The present system may be operated in a less efficient non-catalytic mode of operation during cold start followed thereafter by more efficient catalytic plasma reforming after the catalyst reaches operating temperature. The water/steam may be obtained from oxidation of hydrogen in a fuel cell or by combustion in an engine such as a diesel engine. The water-steam may also be obtained from the exhaust of a diesel engine.
In yet another aspect, the hydrogen rich gas is delivered to a catalytic converter of an internal combustion engine wherein the enthalpy of the hydrogen-rich gas preheats and/or activates the catalyst in the catalytic converter. The hydrogen-rich gas produced by the system of the invention may also be used for reducing processes in metallurgy and chemistry. The hydrogen-rich gases may also be used for hydrogenation as in food processing and fuel upgrading.
In yet another embodiment, the CO content of the reformate is decreased by the use of a non-thermal, catalytic reaction to selectively oxidize the CO to CO2.